Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B3/00—Devices comprising flexible or deformable elements, e.g. comprising elastic tongues or membranes
  • B81B3/0064—Constitution or structural means for improving or controlling the physical properties of a device
  • B81B3/0086—Electrical characteristics, e.g. reducing driving voltage, improving resistance to peak voltage
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G5/00—Capacitors in which the capacitance is varied by mechanical means, e.g. by turning a shaft; Processes of their manufacture
  • H01G5/16—Capacitors in which the capacitance is varied by mechanical means, e.g. by turning a shaft; Processes of their manufacture using variation of distance between electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G5/00—Capacitors in which the capacitance is varied by mechanical means, e.g. by turning a shaft; Processes of their manufacture
  • H01G5/16—Capacitors in which the capacitance is varied by mechanical means, e.g. by turning a shaft; Processes of their manufacture using variation of distance between electrodes
  • H01G5/18—Capacitors in which the capacitance is varied by mechanical means, e.g. by turning a shaft; Processes of their manufacture using variation of distance between electrodes due to change in inclination, e.g. by flexing, by spiral wrapping
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G5/00—Capacitors in which the capacitance is varied by mechanical means, e.g. by turning a shaft; Processes of their manufacture
  • H01G5/38—Multiple capacitors, e.g. ganged
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B2201/00—Specific applications of microelectromechanical systems
  • B81B2201/02—Sensors
  • B81B2201/0221—Variable capacitors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B2203/00—Basic microelectromechanical structures
  • B81B2203/04—Electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H59/00—Electrostatic relays; Electro-adhesion relays
  • H01H59/0009—Electrostatic relays; Electro-adhesion relays making use of micromechanics

Definitions

• Embodiments of the present invention generally relate to a micro- electromechanical system (MEMS) digital variable capacitor (DVC).
• MEMS micro- electromechanical system
• DVC digital variable capacitor
• Some DVC devices are based on a moveable MEMS element with a control-electrode above (i.e., a pull-up or pull-off or PU-electrode) and below (i.e., a pull-in or pull-down or PD-electrode) the moveable MEMS element, as shown schematically in Figure 1 .
• a control-electrode above (i.e., a pull-up or pull-off or PU-electrode) and below (i.e., a pull-in or pull-down or PD-electrode) the moveable MEMS element, as shown schematically in Figure 1 .
• an RF-electrode below the moveable MEMS element (i.e., plate or cantilever or movable plate electrode).
• a voltage is applied to either the PU or PD-electrode, which causes the MEMS element to be pulled-up or pulled-down in contact to provide a stable minimum or maximum capacitance to the
• the capacitance from the moveable element to the RF-electrode (which resides below the moveable element) can be varied from a high capacitance C ma x when pulled to the bottom (See Figure 2) to a low capacitance C m in (See Figure 3) when pulled to the top.
• FIG. 4 shows how the MEMS DVC device is integrated in the Back-end- of-Line (i.e., BEOL) of a complementary metal oxide semiconductor (CMOS) process.
• CMOS complementary metal oxide semiconductor
• a metal shield connected to RFGND i.e., RF-ground
• RFGND i.e., RF-ground
• the metal shield is typically placed in the lower metal levels (e.g., M i ). Additional metal levels M 2 ...M n- i between the metal-shield and the RF-electrode (implemented in M n ) ensure that the parasitic capacitance between the RF and the ground shield is limited.
• Figure 5 shows a top-view of the PD-electrode and RF-electrode of a MEMS DVC cell.
• the RF connection is made at side A of the MEMS DVC cell while the other connections (GND, PU, PD) are made at side B of the MEMS DVC cell.
• Figure 6 shows how multiple MEMS DVC cells are arranged around the RF-pin for optimal RF-performance.
• the CMOS waveform controller that controls the state of the MEMS DVC devices is placed in the same chip, either off to the side or underneath the MEMS cells.
• FIG. 7 schematically shows the electrical connection of the waveform controller to the MEMS DVC cells.
• the moveable element is typically on DC-ground and the voltages applied to the PD-electrode (Vbottom) and to the PU-electrode (Vtop) are typically controlled to ensure a long-life stable performance of the MEMS DVC device.
• the resistors Rpd and Rpu provide for isolation between the RF- signals present on the PU and PD electrode and the CMOS drivers. This also ensures no CMOS noise is coupled into the RF electrode of the MEMS DVC cells.
• these resistors provide for damping of the MEMS devices within the MEMS DVC cells which allows for fast operation.
• these resistors are generated with high-resistivity poly-silicon and values of these resistors range from 50kQ to 10 ⁇ .
• Figure 8 shows a cross-section of the MEMS DVC device near side B of the MEMS DVC cell.
• a connection is made between the poly-resistor and the PD- electrode to allow the CMOS waveform controller to apply voltages to each MEMS DVC cell while maintaining the isolation between the RF-signals and the CMOS signals.
• a hole is created in the ground-shield to allow the connection to the poly- resistor Rpd.
• a similar connection is made between the PU-electrode and the poly- resistor Rpu. Any noise present in the CMOS substrate can couple into the poly- resistor and subsequently couple into the PD and PU-electrode. This noise can subsequently couple into the RF-electrode and impact the RF-performance of the device.
• substrate ground-contacts can be avoided near the MEMS DVC devices, so that any CMOS noise generated in the CMOS waveform controller that sits adjacent to the MEMS devices in the chip (See Figure 6) has to travel some distance through the CMOS substrate before it reaches the poly-resistor.
• Substrate ground-contacts are not required in the region of the MEMS devices since there are no active devices in the silicon substrate in this region.
• FIG. 9 shows a simplified equivalent circuit model of the poly-resistors Rpu, Rpd of a given MEMS DVC cell with parasitic capacitors Cshield to the RFGND-shield and parasitic capacitors Csub to the substrate.
• the voltages Vtop, Vbottom are generated by the CMOS waveform controller with respect to the CMOS ground, which is also tied to the substrate.
• any current coupled to the substrate through Csub has to travel through the substrate for a certain distance before the actual CMOS ground reference point is reached, i.e. there is a given series resistance Rsub.
• the current coupled to the RFGND shield is effectively directly coupled to the CMOS ground because the RFGND is tied to the CMOS GND either inside or outside the chip (indicated by the dotted line).
• the coupling of the poly-resistors to the substrate Csub can be larger than the coupling of the poly-resistor to the metal- shield Cshield above the poly-resistors. This means that the dynamic response of the poly-resistors will depend on the values of Csub and Rsub.
• Each MEMS cell in Figure 6 has a poly-resistor near side B of the cell to provide RF-isolation and MEMS-damping. Since each MEMS cell is located at a different position inside the chip, the value of Rsub can vary greatly from cell to cell. This means the various cells will exhibit a different RF-isolation and damping and also a different dynamic actuation of the various MEMS-cells on the chip.
• the present invention generally relates to a MEMS DVC.
• the MEMS DVC has an RF electrode and is formed above a CMOS substrate.
• a poly-resistor that is connected between a waveform controller and the electrodes of the MEMS element, may be surrounded by an isolated p-well or an isolated n-well.
• the isolated well is coupled to an RF ground shield that is disposed between the poly-resistor and the MEMS element. Due to the presence of the isolated well that surrounds the poly-resistor, the substrate resistance does not influence the dynamic behavior of each MEMS element in the MEMS DVC and noise in the RF signal is reduced.
• a MEMS DVC comprises a substrate; a MEMS device disposed above the substrate, the MEMS device having an RF electrode and one or more other electrodes; a poly-resistor disposed between the substrate and the MEMS device and coupled to the MEMS device; a RF ground shield disposed between the MEMS device and the poly-resistor; a p-well contact disposed between the substrate and the poly-resistor, wherein the p-well contact is coupled to the RF ground shield; an isolated p-well coupled to the p-well contact and disposed between the substrate and the poly-resistor, wherein the p-well contact and the isolated p-well surround the poly-resistor; an n-well contact disposed between the substrate and the poly-resistor, wherein the n-well contact is coupled to the RF ground shield; and an n-well coupled to the n-well contact and disposed between the substrate and the isolated p-well, wherein the n-well contact is coupled to
• a MEMS DVC comprises a MEMS device disposed above a substrate, the MEMS device having one or more electrodes; a first poly-resistor coupled to at least one of the one or more electrodes; an n-well surrounding the first poly-resistor; and an RF ground shield coupled to the n-well.
• MEMS DVC comprises a substrate; a deep n-well embedded within the substrate; a first isolated p-well disposed above the deep n- well; a first poly-resistor disposed above the isolated p-well and coupled to a MEMS device; and an RF ground shield disposed between the poly-resistor and the MEMS device, wherein the deep n-well and the isolated p-well are coupled to the RF ground shield.
• Figure 1 is a schematic cross-sectional illustration of a MEMS DVC in the free standing state.
• Figure 2 is a schematic cross-sectional illustration of the MEMS DVC of Figure 1 in the C max state.
• Figure 3 is a schematic cross-sectional illustration of the MEMS DVC of Figure 1 in the C m in state.
• Figure 4 is a schematic cross-sectional illustration of a MEMS DVC device with an M1 ground shield underneath the MEMS device to shield the silicon substrate from the RF.
• Figure 5 is a schematic top-view of a MEMS DVC cell with the RF connection on a first side of the cell and the ground and pull-down connections on the opposite side of the cell.
• Figure 6 is a schematic top-view of a DVC-chip with MEMS DVC cells arranged around an RF-pin and a CMOS waveform controller located on the same chip.
• Figure 7 is a schematic illustration of the electrical connection of a MEMS DVC with poly-resistors Rpu and Rpd.
• Figure 8 is a schematic cross-sectional illustration of a MEMS DVC near a side of the cell with the connection of the pull-down electrode to the poly-resistor.
• Figure 9 is a circuit diagram of the MEMS DVC of Figure 8.
• Figure 10 is a schematic cross-sectional illustration of an isolated p-well underneath a poly-resistor in a MEMS DVC.
• Figure 1 1 A is a schematic top view of the poly-resistors with an isolated p- well according to one embodiment.
• Figure 1 1 B is a schematic top view of the poly-resistors with an isolated p- wells according to another embodiment.
• Figure 12 is a circuit diagram of the MEMS DVC of Figure 10.
• Figure 13 is a schematic cross-sectional illustration of an isolated n-well underneath a poly-resistor in a MEMS DVC.
• Figure 14 is a schematic top view of the poly-resistors with an isolated n- well according to one embodiment.
• Figure 15 is a circuit diagram of the MEMS DVC of Figure 13.
• the present invention generally relates to a MEMS DVC.
• the MEMS DVC has an RF electrode and is formed above a CMOS substrate.
• a poly-resistor that is connected between a waveform controller and the electrodes of the MEMS element, may be surrounded by an isolated p-well or an isolated n-well.
• the isolated well is coupled to an RF ground shield that is disposed between the poly-resistor and the MEMS element. Due to the presence of the isolated well that surrounds the poly-resistor, the substrate resistance does not influence the dynamic behavior of each MEMS element in the MEMS DVC and noise in the RF signal is reduced.
• each MEMS cell will have an identical dynamic performance when programming/erasing the bit which makes it easier to match the switch times between cells in the array, which allows for an easier optimization of the switch- times of the MEMS cells.
• Figure 10 shows one embodiment of the invention, where an isolated P- well underneath the poly-resistors is used which is electrically connected to the metaH RFGND-shield located above the poly-resistor.
• the isolated P-well is commonly available in triple-well CMOS processes.
• the poly-resistor is surrounded by a complete N-well guard-ring.
• a deep N-well implant is used to create an isolated P-well which is surrounded on the bottom and on the sides by an N-region. This allows the isolated P-well to be biased separately from the P-substrate underneath. This facilitates the connection of the isolated P-well to the RFGND shield.
• the N- well and Deep N-well are also connected to the RFGND shield, effectively shorting the pn-diode of the isolated P-well and the N-well guardring.
• Figure 1 1A shows a top-view of the poly-resistors located above the isolated P-well.
• the MetaH RFGND shield (omitted in Figure 1 1A for clarity) connects to the N+ active connections of the N-well guard-ring and to the P+ active connections of the isolated P-well. It contains holes to provide access to the poly- resistor connections (Vtop, Vbottom, Vpu, Vpd).
• a P+ active isolated P-well connection is surrounding each poly-resistor to pick up any current coupled into the isolated P-well and redirects this current to the MetaH RFGND-shield.
• Both poly-resistors of the DVC-cell ⁇ Rpu, Rpd) share the same isolated P-well.
• each resistor could also be positioned inside a separate isolated P-well.
• Figure 12 shows a simplified equivalent electrical circuit model of the poly- resistors Rpu, Rpd with parasitic capacitors Cshield to the RFGND-shield and parasitic capacitors Cpwell to the isolated P-well underneath. Any current coupled from the poly-resistor to the isolated P-well through Cpwell is now directly coupled to the RFGND via the isolated P-well contact. Because the RFGND is connected to the CMOS ground either inside or outside the chip (indicated by the dotted line) the substrate resistance Rsub no longer influences the dynamic behavior and each DVC cell will behave similarly independent of its location in the chip. The substrate contacts can therefore be located in the CMOS region of the chip and do not have to be placed near the MEMS cell.
• any CMOS noise in the substrate has to travel some distance through Rsub before it reaches the poly-resistor region of each DVC cell. It will couple into the isolated P-well through the diode Dnwell between the substrate and the Nwell/deep-Nwell regions. However, because the isolated p-well and Nwell/deep- Nwell are coupled to RFGND and directly to the CMOS ground outside the chip, this coupling has no influence on the spurious noise in the RF-electrode of the DVC device. Therefore the isolated P-well also provides for an improved noise performance of the DVC device.
• Figure 13 shows another embodiment of the invention, where the isolated P-well underneath the poly-resistors is not present, but, rather, the N-well is used.
• the N-well is connected to the metaH RFGND-shield located above the poly- resistor.
• the metal layers above have been omitted but it is to be understood that additional metal layers, such as those shown in Figure 4, may be present.
• the arrangement allows the N-well to be biased separately from the P- substrate underneath, which facilitates the connection of the N-well to the RFGND shield.
• the n-well has an inner wall that isolates the two poly-resistors from one another.
• Figure 14 shows a top-view of the poly-resistors located above the N-well.
• the MetaH RFGND shield (omitted in Figure 14 for clarity) contains holes to provide access to the poly-resistor connections (Vtop, Vbottom, Vpu, Vpd).
• Figure 14 also shows a surface implant region that is coupled to the N-well.
• the surface implant region is a very shallow surface n+ implant region that provides a low-ohmic connection to the N-well.
• Figure 15 shows a simplified equivalent electrical circuit model of the poly- resistors Rpu, Rpd with parasitic capacitors Cshield to the RFGND-shield and parasitic capacitors Cnwell to the N-well underneath. Any current coupled from the poly-resistor to the n-well through Cnwell is now directly coupled to the RFGND. Because the RFGND is connected to the CMOS ground either inside or outside the chip (indicated by the dotted line) the substrate resistance Rsub no longer influences the dynamic behavior and each DVC cell will behave similarly independent of its location in the chip. The substrate contacts can therefore be located in the CMOS region of the chip and do not have to be placed near the MEMS cell.
• any CMOS noise in the substrate has to travel some distance through Rsub before it reaches the poly-resistor region of each DVC cell. It will couple into the N-well through the diode Dnwell. However, because the N-well is coupled to RFGND and directly to the CMOS ground outside the chip, this coupling has no influence on the spurious noise in the RF-electrode of the DVC device. Therefore the N-well by itself without the isolated P-well also provides for an improved noise performance of the DVC device.

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• 2014
  • 2014-05-30 WO PCT/US2014/040235 patent/WO2015009360A1/en active Application Filing
  • 2014-05-30 CN CN201480032389.6A patent/CN105263853B/zh active Active
  • 2014-05-30 EP EP14734335.4A patent/EP3003964B1/en active Active
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